The present invention relates to an Image reading apparatus.
An image reading apparatus (see JP-A-2001-133906) mounted with a contact image sensor module has heretofore been known. Since an optical system of the contact image sensor module has a short optical path, it is easy to reduce the size of the image reading apparatus.
However, since the contact image sensor module has a shallow depth field, the image reading apparatus cannot clearly read a document placed at a position away from a platen surface of a document platen. For example, an image reading apparatus described in JP-A-2001-133906 cannot clearly read a 35 mm film or the like held by a holder.
Image reading apparatuses described in JP-A-2003-37712 and JP-A-2003-37713, each including a plurality of optical systems, can clearly read a reflective document and a transmissive document by changing an optical path in response to the document However, the image reading apparatuses described in JP-A-2003-37712 and JP-A-2003-37713, the optical systems of which have a complex configuration and a long optical path, have the problem in which they are high in manufacturing cost and unfit for a reduction in size.
A first linear image sensor and a second linear image sensor are disposed to provide a configuration such that an optical image of a document placed on the platen surface of the document platen is focused onto the first linear image sensor, and such that an optical image of a document placed at a position away from the platen surface of the document platen is focused onto the second linear image sensor. Such a configuration makes it possible to clearly read the document placed on the platen surface of the document platen and the document placed at a position away from the platen surface of the document platen.
Meanwhile, in the contact image sensor module, there are some cases where an error occurs in the distance between the linear image sensors and the document platen, and an image is blurred due to the error. In this case, the configuration can be such that, when the contact image sensor module has only one linear image sensor, a clear image is focused by adjusting the aforesaid distance with spacers inserted between the linear image sensors and the document platen.
However, when the contact image sensor module has the first and second linear image sensors, there are some cases where an error occurs in different ways between the first and second linear image sensors. Thus, there is the problem in which, even when a clear image becomes focused onto one of the linear image sensors after the distance is adjusted, it is not necessarily the case that a clear image is also focused onto the other linear image sensor